It is frequently said that the 50mm is a normal field of view. Does this come from a FF perspective or a crop sensor?

Thanks for any answers.

As others have noted, 50mm has long been considered a "normal" lens for 35mm film and full-frame digital cameras. For APS-C sensors, 30 or 35mm lenses are generally considered normal. Four Thirds is 25mm, and a 6 X 6 roll-film camera will likely have about an 80mm lens as normal. Tamron has a page on lens fundamentals; they note, as some posters above have already mentioned, that "normal" isn't necessarily just one focal length, but can include a range. For example, with respect to the 35mm format, they say, "Generally speaking, a focal length range that provides a similar perspective to the human eye is considered to be somewhere between 40-60mm." Below are a few other excerpts on the subject of normal lenses:

"A photographic lens provides a visual effect, making closely located subjects larger while remotely located subjects smaller. As the focal length becomes shorter in a wideangle lens, this perspective difference expands making closely located subjects even bigger and remotely located ones even smaller (exaggerated perspective). In contrast, in a telephoto lens, as focal lengths become longer, less difference is observed between close and distant subjects, making it appear as if they are closer regardless of the distance between them(compressed perspective)."

Pretty much everything from that tamron article is wrong. The second paragraph is totally and completely wrong. There's even an article here on DPR that's dedicated to demonstrating that it's wrong.